A semiconductor device is an active element-including electronic device using electrical characteristics of a semiconductor. Such a semiconductor device has been widely used in an audio device, a communication device, a computer, an electric appliance and the like. Among these, a semiconductor device including a three-terminal active element such as a thin film transistor (hereinafter, also referred to as a “TFT”), a MOS (Metal Oxide Semiconductor) transistor has been used as a switching element formed in each pixel, a control circuit for controlling each pixel, in a display device such as an active matrix liquid crystal display device (hereinafter, also referred to as a “liquid crystal display”). Such a semiconductor device permits a higher-definition display device and enables such a display device to fast display moving images.
A liquid crystal display including a peripheral driving circuit such as a driving circuit and a control circuit integrally formed with a pixel part, a so-called monolithic liquid crystal display (hereinafter, also referred to as a “system liquid crystal”) has been brought to attention (for example, refer to Patent Documents 1 and 2). According to a semiconductor device used in such a system liquid crystal, the switching element in the pixel part and the peripheral driver circuit are simultaneously formed on the same substrate. Accordingly, the number of components is significantly reduced and an assembling step, an examination step and the like of the liquid crystal display device can be reduced. As a result, a reduction in production costs and an improvement in reliability are permitted.
For a display device such as a liquid crystal display device, a reduction in electric power consumption and an improvement in performances such as a higher-definition image and a high-speed image display are strongly needed. A reduction in a space for the peripheral driver in the system liquid crystal is also needed.
Therefore, for a semiconductor device used in a display device, each element strongly needs to be further finely formed. In order to form more elements in a limited area, a design rule of a submicron order, that is, a pattern definition that is fine enough to be adopted to an integrated circuit (hereinafter, also referred to as an “IC”), is needed for the peripheral driver circuit. Further, a semiconductor element in the peripheral driver circuit needs to improve a carrier mobility of a semiconductor layer. Because of this need, the semiconductor element must be finely formed.
However, according to a conventional production process of forming a semiconductor device directly on a glass substrate, the glass substrate has insufficient heat resistance and therefore it might be distorted in a heat treatment step during production processes. Therefore, a desired circuit pattern of submicron order cannot be formed. Further, the glass substrate used for producing a liquid crystal display device such as a system liquid crystal has become larger. Therefore, the glass substrate surface is more easily distorted during the production processes.
For this problem, a technology of transferring a driver IC on a liquid crystal display substrate using a SOI (Silicon On Insulator) substrate in which a driver IC is formed in a single crystal silicon layer formed on an electrical insulator (for example, refer to Patent Document 3). According to this, an IC including a semiconductor element such as a MIS (Metal Insulator Semiconductor) can be formed through a conventional IC tip preparation step. Therefore, a semiconductor device including a fine and high-performance IC having a desired circuit design of submicron order can be produced. However, a step of preparing the SOI substrate is separately needed, which complicates the production processes and increases the production costs. In such a point, there is room for improvement.
Thus, the IC used in a peripheral driver of a system liquid crystal needs to be inexpensively produced by simple production processes. Further, in such an IC, an improvement in performances and a reduction in an electric power consumption needs to be realized by, for example, finely forming an element and a circuit pattern.
[Patent Document]
    Japanese Kokai Publication No. Hei-06-37313[Patent Document 2]    Japanese Kokai Publication No. 2000-36598[Patent Document 3]    Japanese Kokai Publication No. Hei-06-75244